On my now older e-bike (Trek XM700+) with the Bosch system, I tend to operate it like another set of gears. Cadence slowing down due to a hill? Turn on, or bump up, the power assist. Going down? Bump down the assist, or turn it off. Overall, my average speed is faster, due to the assist. One article I read said that in limited testing, riders on e-bikes tended to burn 30% fewer calories over the same distance as compared to conventional bikes. But they tended to go much further. So it all roughly evens out in the end. I now go places and distances I never would have considered, and put more time in the saddle. I do find that by fall I use the power assist far less than I do in the spring...so I must be getting to some higher level of fitness...